Guadalupe Hidalgo, Treaty of(Feb. 2, 1848), treaty between the United States and Mexico that ended the Mexican War. It was signed at Villa de Guadalupe Hidalgo, which is a northern neighbourhood of Mexico City. The treaty drew the boundary between the United States and Mexico at the Rio Grande and the Gila River; for a payment of $15,000,000 the United States received more than 525,000 square miles (1,360,000 square km) of land (now Arizona, California, western Colorado, Nevada, New Mexico, Texas, and Utah) from Mexico and in return agreed to settle the more than $3,000,000 in claims made by U.S. citizens against Mexico. (See primary source document: Treaty of Guadalupe Hidalgo.) With this annexation, the continental expansion of the United States was completed except for the land added in the Gadsden Purchase (1853).

The treaty helped precipitate civil war in both Mexico and the United States. In Mexico it left many citizens unsure of their country’s future as an independent state; political extremism followed, and civil war broke out at the end of 1857. The expansion of slavery in the United States had been settled by the Missouri Compromise (1820), but addition of the vast Mexican tract as new U.S. territory reopened the question. Attempts to settle it led to the uneasy Compromise of 1850 and the Kansas–Nebraska Act (1854).